Field of the Invention
The present invention relates to a pneumatic tire which can discharge static electricity generated in a vehicle body or the tire, and a manufacturing method of the pneumatic tire.
Description of the Related Art
In recent years, there have been proposed a pneumatic tire including a tread rubber blended with silica at a high ratio in order to reduce the rolling resistance that largely affects the fuel consumption of a vehicle and to increase braking performance on a wet road surface. However, compared to a tread rubber blended with carbon black at a high ratio, the electric resistance of such tread rubber is high, and accordingly, static charge generated on a vehicle body or the tire is prevented from being released to the road surface. As a result, problems like radio noises tend to occur.
Accordingly, there has been developed a pneumatic tire structured such that an electrical conduction performance can be achieved by partly arranging a conductive rubber blended with a carbon black in a tread rubber constructed by a non-conductive rubber blended with a silica so as to set a conductive route. Without being limited to the tread rubber, the other rubber members for the tire such as a side wall rubber can be formed by the non-conductive rubber. In such case, the conductive route is provided in the rubber member.
Further, there has been known a so-called ribbon winding construction method of forming a rubber ribbon winding body by continuously feeding an uncured rubber ribbon to a wound body such as a forming drum and spirally winding the rubber ribbon. According to the ribbon winding construction method, various cross sectional shapes can be easily formed by appropriately adjusting a winding condition. In addition, the rubber member constructed by the rubber ribbon winding body does not have any joint portion which generates a great step, and is more excellent in a uniformity in comparison with a rubber member which is formed by integrally extruding.
The ribbon winding construction method can be utilized for forming the rubber member having the conductive route mentioned above, for example, as shown in Patent Documents 1-3. However, in the case that an amount of the conductive rubber is reduced for enhancing an effect of lowering a rolling resistance, connection of the conductive rubber becomes insufficient in a ribbon interface, in the winding operation which partly overlaps the rubber ribbons, which are adjacent in a width direction, with each other and connects the conductive rubber between them, so that the conductive route tends to be disconnected. Further, since the disconnection in the ribbon interface is continued along a tire circumferential direction, there has been a risk that the disconnection is an obstacle to the electrical conduction performance.